I developed a web service for uploading files to the server, this web service will be used by 45k users approximately.

I started to load test my application with JMeter and I'm a newbie in software performance.

I tested with different values in Thread Group (Number of Threads and Rump-Up Period) ex: 1000 and 200, 1000 and 300. I see always all requests response are "200 OK" but I don't find all requests files stored in the folder (generally the number of files found is equal to the Rump-Up Period).

45,000 users at the same time or in total? I have heard that a single box can only handle 200-300 threads so you are probably not really simulating 1000 users unless you are using more than one server to send requests. If you set thread group to say 100 does it consistently work then?

Thank you for your response. I need to know the max number of users that could simultaneously invoke this web service, is that the good way to know that? Yes it does work but only with an equal number of Number of Threads and Ramp-Up Period, so what is the relationship between them?
– Mane_87Jan 24 '17 at 9:13

ramp up is the time it takes to have all threads active. So if I have 100 threads with 100 ramp up it will spin up approximately 10 threads every 10 seconds. If increasing the ramp up makes it work better it means the system cannot really handle the number of threads you are trying to hit it with. If the response is returning a 200 when you think it actually failed I would check the server for error logs.
– David CainJan 24 '17 at 18:00